Follow from Mastodon

When you enter your website address, my website will fetch your page and look for a rel=subscribe link. This indicates where my site should send you to confirm and create the subscription. After finding your subscription endpoint, you will be redirected there to confirm the subscription at your website. It's up to your software to actually subscribe to my website.

Add either an HTTP header or HTML tag like the below, and the URL you're subscribing to will be added as the subscribe-to query string parameter,e.g. ?subscribe-to=http://aaronparecki.com/